Piston devices are preferably used where a large fluid pressure difference needs to be induced or utilized. Commonly employed linearly oscillating piston pumps, compressors and engines are well known for their mechanical friction losses, fluid friction losses and thermodynamic losses. Mechanical friction losses particularly in engines are attributed to the commonly large number of valves, pistons and their driving and linking mechanisms and the friction in between them. Fluid friction losses occur predominantly across intake and exhaust valves. Thermodynamic losses are contributed by the initial fluid compression taking place in the hot combustion chamber where the working fluid under compression is additionally heated from outside. As the working fluid also heats up internally during its compression, the compression ratio is reduced by the external heating in a gasoline engine by the self ignition temperature of the gasoline vapors. In a diesel engine well known chemical reaction temperatures limit the maximum compression ratio. Thermodynamic efficiency is directly related to compression ratio as is well known in the art. Therefore there exists a need for a piston device that may be utilized as a pump, compressor and/or in a combustion engine and that provides reduced mechanical friction losses due to a reduced number of moving parts, reduced fluid friction losses due to a fluid exchange control without valves and in case of a combustion engine reduced thermodynamic losses due to a compression stage that is structurally separated from combustion heated structures. The present invention addresses these needs.
The concept of a rotating volume that contracts and expands while moving in a loop has been considered in the prior art to provide fluid exchange without valves. The well known Wankel engine is the only mass produced rotating piston combustion engine to date. Despite its compact design without valves, it has the fundamental flaw of a line contact seal that slides along an abruptly changing peripheral surface with high velocity. This limits live time as well as compression ratio. Therefore, there exists a need for a rotating piston engine that provides area sealing in between continuously shaped sealing surfaces for a reliable lasting operation. The present invention addresses also this need.
Other rotating piston engine concepts in the prior art provide work volumes that expand and contract while rotating. On the one hand, these engine concepts fail to address the particular needs for a simple mechanical drive with a low number of joints and the shortest mechanical force transmitting paths that can be designed with sufficient strength and stiffness and yet with minimal moving mass and mass forces. Also it is desirable to have all moving masses at a minimum and substantially balanced to minimize vibration and bearing loads at high rotational speeds. This is one well known prerequisite to drive such devices with sufficiently high rotational speeds in order to obtain a power-to-weight ratio of such an engine that is at least comparable with that of a modern oscillating piston engine. Therefore, there exists a need for a rotating piston device that is mechanically simple with a low number of lightweight moving parts and with substantially balanced rotating masses for high rotational speeds and consequently for a high power-to-weight ratio. The present invention addresses also this need.
On the other hand, to employ a rotary piston device in conjunction with hot combusting fluids, there is a need to provide the pistons particularly with a sufficiently loose connection, cooling and lubrication so that they their thermal expansion and sliding friction may be conveniently controlled. At the same time pistons and other parts contributing in encapsulating the work volumes are desired to have area contact in the sliding seal interfaces. This is another prerequisite for reliable sealing at high pressures, minimized wear and optimized heat transfer in the sliding seal interfaces. The present invention addresses also these needs.